Explosive growth in demand for telecommunication services, from both the private as well as commercial sectors, has placed an unprecedented strain upon currently available telecommunications networks. Without alternative network delivery technologies and topologies, overall effective network speed is likely to be reduced while occurrences of bottlenecks within networks will become increasingly frequent.
Bi-directional, free-space optical (FSO) communications networks can, where feasible, provide a useful alternative to microwave links, wire, or cable system applications. Such networks can be transparent to current as well as future network architectures due to sharing of common technological platforms with fiber optic transmission systems, the backbone of many present day telecommunication systems. FSO communication systems can generally share common fiber-optic components, and commercial optical components can often utilized for both applications. The primary difference in free-space optical data link systems is that the medium of propagation is the atmosphere rather than optical fiber.
Utilizing current state-of-the art fiber-optic components, free-space optical data links can be fully integrated into current short-haul and long-haul high-speed optical networks. Free-space data links can fully attain current synchronous optical networking (SONET) system architectures, such as for example SONET OC-48 architectures utilizing current 1550 nm technology platforms. Additionally, such systems can be scaled to higher data rates and configurations. Optical data link systems can benefit from operating in an unregulated segment of the electro-magnetic spectrum. Unlike the microwave and RF spectrum, optical data links can generally require no special leasing fees or tariffs to be issued. Additionally, because of the operating wavelength of the system, issues related to eye safety can generally be minimized. Furthermore, no special precautions or permits are typically required operating a free-space data link related to territorial right-of-ways. Expenses related to plowing and trenching of fixed cabled systems can also be avoided.
More recently, FSO communication technology has leveraged commercial advancements made within the 1550 nm optical transmission band. Erbium fiber doped amplifier (EFDA) technology has been incorporated within system design configuration for enhancing the overall effective optical budget of transport budgets and thereby extending the reach of transport systems over the air.
High power optical amplifiers are useful for terrestrial free-space transmission as well as fiber optic systems. Repeater distances have been extended in terrestrial and submarine fiber systems and dense wavelength division multiplexing (DWDM) transmission architectures have been introduced. With the advent of high power Er/Yb optical amplifiers, similar advances as seen in fiber optic transmission have also been realized in optical wireless and free-space laser communications systems. Experimental transmission results for a single-channel 1550 nm free-space optical data-link operating at 2.5 Gbps over a 2.4 km transmission span have been reported, as have results for a four-channel 1550 nm wavelength division multiplexing (WDM) free-space optical data link operating at 10 Gbps over a 4.4 km transmission distance.